The present invention relates to a large-aperture telephotographic lens of high performance having F.sub.NO of 1:1.8-2, and an angle of view on the order of 18.degree..
One generally used telephoto lens having an angle of view on the order of 18.degree. is known as an Ernostar-type telephoto lens. This type of telephoto lens has improved aberrations normally at F.sub.NO of 1:2.8. However, with telephoto lenses having larger apertures such as F.sub.NO of 1:1.8-2, the spherical aberration is increased and is overly compensated for with respect to light having short wavelengths (for example, in the vicinity of g-line 436 nm). There are known large-diameter telephoto lenses which have coped with such problems by thickening front-group lenses or using a doublet in the front lens group. However, the prior telephoto lenses have proven unsatisfactory in performance. Furthermore, since large-aperture lenses are subjected to increased variations in various aberrations dependent on the positions of objects, it has been quite difficult to keep required high performance over a wide range from the infinite distance to close positions.